1. Field of the Invention
The present invention relates to a safety band for a CRT(Cathode Ray Tube), and in particular to a safety band for a CRT which is capable of enhancing a stability of use by providing a straight line shape safety band having a reinforced anti-explosive characteristic for each panel in a cathode ray tube in which a flat type panel and an effective screen expanded panel, which attract a big attention, are adapted.
2. Description of the Background Art
The CRT(Cathode Ray Tube) is directed to a display apparatus which is widely used for a television set, an oscilloscope, a radar system, etc.
In the above-described cathode ray tube, there are provided fluorescent pixels which are a light emitting device for converting a received electrical image data into a visual data, and a graphite which is a light absorbing material. A color image which is reproduced by impacting an electronic beam onto a fluorescent film formed of an aluminum film for enhancing a luminance, so that a human can view a color image.
As shown in FIG. 1, the conventional CRT includes a panel 1 installed on a front surface, and a conical funnel 2 melted at a rear end of the panel 1 for thereby forming a vacuum container of a CRT.
An electron gun 5 is installed at an end portion having a small diameter among the portions of the funnel 2, namely, in the interior of a neck portion 3. A deflection yoke is installed at an outer portion near the neck portion 3 for deflecting the emitted electron beam 4 onto the whole portions of a screen by generating a fin cushion shaped horizontal deflection magnetic field and a barrel shaped vertical deflection magnetic field.
In addition, a fluorescent film 6 is formed on an inner surface of the panel 1, and a shadow mask 7 which operates for a function of a section-based electrode of the electron beam 4 at a certain distance from the fluorescent film 6 is stably engaged by a frame 8 installed therein.
In the above-described conventional cathode ray tube, the electron beam 4 outputted from the electron gun 5 is deflected onto a certain portion of the screen by the vertical and horizontal deflection magnetic fields and continuously passes through a plurality of through holes(not shown) formed at the shadow mask 7 and impacts the fluorescent film 6 for thereby implementing a certain image.
In addition, the interior of the conventional CRT has a vacuum state therein by the panel 1 and the funnel 2. A certain stress occurs at the panel 1 by an external atmospheric pressure. As shown in FIG. 2, a compression pressure occurs at the front surface of the panel based on the structural characteristic of the CRT, and a tension stress occurs at a side wall of the panel 1.
Therefore, in a state that the compression stress and the tension stress are formed based on the vacuum, when an external impact is applied to the CRT, a certain exploding phenomenon that the panel 1 or the funnel 2 is exploded may occur. The above-described exploding phenomenon cause a malfunction of the CRT and a user may be damaged.
Since the glass which is a material of the panel 1 is weak against a tension stress compared to the compression stress, the side wall of the panel 1 is weaker than the front portion of the same.
Here, the above-described exploding phenomenon is classified into four steps. The above-described steps will be explained with reference to FIG. 3D.
First, in a first step which is an initial crack forming step, when a certain portion of the CRT is impacted by an external impact source 10, as shown in FIG. 3A, a small crack occurs at the panel 1.
Namely, when the strength of the impact portion exceeds a certain level against the external impact source 10, a small crack occurs by the compression and tension stresses. The impact energy is spread over the CRT At this time, the crack grows at a structurally weal portion of the CRT or at a skirt which receives a concentrated stress.
In a second step which is a crack growing step, as shown in FIG. 3B, a crack xe2x80x9ccxe2x80x9d grows in the direction skirt of the panel 1, and the crack grows in a radial or conical shape.
The thusly formed creaks are grown over the entire portions of the CRT. At this time, the crack is increased more at the skirt portion to which the tension stress is applied, so that the skirt portion is expanded.
In a third step, as shown in FIG. 3C, the panel or the funnel 2 are depressed. The crack xe2x80x9ccxe2x80x9d is extended from the outer surface to the inner surface of the panel 1, so that the surface of the panel 1 or the funnel 2 is depressed.
As the skirt portion is expanded, the cracks are increased, and then a glass(the surface of the panel) is depressed due to a pressure difference between the inner and outer portions of the CRT.
In a fourth step, as shown in FIG. 3D, the particles are spread. When the CRT is inwardly depressed, a certain kinetic energy is generated, and the particles collide with each other, so that the particles are outwardly spread.
In a usual case, the surface portion is depressed, and then a certain impact is applied to the funnel 2, and at the final stage, the particles are spread.
As described above, since the exploding phenomenon causes a malfunction of the CRT or a certain damage to a user, so that a safety band 11 is used for preventing the above-described exploding phenomenon.
FIG. 4 is a view illustrating a comparison of the stress before and after the safety band is engaged to the CRT In FIG. 4, the left side illustrates a stress distribution before the safety band is engaged, and the right side illustrates a stress distribution after the safety band is engaged.
Namely, it is possible to enhance a strength of the lateral side by engaging the safety band to the side wall of the panel 1 for thereby preventing an exploding phenomenon.
In detail, when a certain impact is applied to the surface of the CRT a transform stress which expands the side wall portions of the panel 1, namely, a tension stress occurs. In this case, since the side wall portions of the panel 1 is compressed by the safety band 11, so that the cracks xe2x80x9ccxe2x80x9d which pass through the lateral sides and surfaces are prevented for thereby decreasing the speed of the crack xe2x80x9ccxe2x80x9d.
As the safety band 11 is engaged, since a vacuum transformation stress affects the vacuum transformation stress, the direction of the main stress of the surface of the panel 1 is changed, and the growing direction of the crack xe2x80x9ccxe2x80x9d is changed for thereby preventing an explosion.
The safety band 11 surrounds a mold match line which is naturally formed when installing the panel 1. As shown in FIGS. 5A through 5C, the safety band 11 may be formed in a straight line shape 11a, an overlapped shape 11b, a bent shape 11c, etc.
The advantages and disadvantages of each of the safety band 11a, 11b and 11c are compared in the following Table 1.
As shown in Table 1, in the case of the bent type band 11c, the anti-explosion characteristic is excellent. However, the bent type band 11c has a bad processing characteristic, a unit cost, a facility co-usability, a welding method, a welding plate use, a facility investment cost, a productivity per day, etc. compared to the other types. In the case of the straight line type band 11a, the above-described characteristics except for the anti-explosion characteristic is excellent.
Recently, the size of the screen is increased, the use of the flat type screen is increased. Therefore, a new type panel satisfying the above-described trends is introduced. As the new type panel, FIG. 6A illustrates a conventional panel, FIG. 6B illustrates a panel(FCD) 100 having a flat outer surface and a curved inner surface, and FIG. 6C illustrates a panel 200 obtained by increasing the size of the effective screen.
Namely, the FCD panel 100 is capable of providing a high resolution compared to the conventional curved type panel 1 for thereby implementing a refine resolution. The panel 200 obtained by increasing the size of the effective screen has an advantage in that it is possible to view a wider screen compared to the conventional panel even when the sizes of the panels are same.
However, the above-described FCD panel and the panel obtained by increasing the size of the effective screen have a low structural strength compared to the conventional curved panel for the reasons that the strength of the FCD panel is weak and has a large thickness difference between the center portion and the corner portion compared to the conventional panel and is weak against the thermal transformation stress with respect to the thermal expansion. In addition, in the panel formed by expanding the effective screen, the cornet portion of the panel must be designed to have a small curvature, so that the stress is concentrated at the corner portion, whereby the anti-explosion characteristic is decreased compared to the panel.
Therefore, it is preferred to install the safety band having an increased anti-explosion characteristic at the CRT in which the FCD panel or the panel formed by expanding the effective screen is adapted.
Namely, in the CRT in which the FCD or the panel formed by expanding the effective screen, an overlapping type band or bent type band which has a good anti-explosion characteristic compared to the straight line type band is preferably used. However, the overlapping type band or the bent type band has a disadvantage in that the processing ability, unit cost, facility co-usability, welding method, the use of welding plate, productivity per day, etc. are bad.
Accordingly, it is an object of the present invention to provide a safety band for a CRT which is capable of increasing a stability of use by enhancing an anti-explosion characteristic based on an optimum band size corresponding to each panel by engaging a safety band to a CRT in which a FCD or a panel obtained by expanding an effective screen is adapted.
It is another object of the present invention to provide a safety band for a CRT which is capable of enhancing a marketing compatibility of system by engaging a straight line shape safety band corresponding to the standard of UL/CSA.
It is another object of the present invention to provide a safety band for a CRT which has a low cost and high efficiency by using a straight line shape band.
To achieve the above objects, there is provided a CRT(Cathode Ray Tube) safety band which satisfies an expression of inequality of 30.16(%)xe2x89xa6D/Wxc3x97100xe2x89xa641.27(%) where W represents the entire width, D represents a width from a front end portion in the width direction to the bent portion in the CRT including a panel having an outer flat surface and an inner surface having a certain curvature, and a safety band bent at a mold match line of a side wall portion of the panel and continuously surrounding a side wall portion of the panel in the lengthy direction.
To achieve the above objects, there is provided a CRT(Cathode Ray Tube) safety band which satisfies an expression of inequality of 17.86(%)xe2x89xa6D/Wxc3x97100xe2x89xa625.00(%) where W represents the entire width, D represents a width from a front end portion in the width direction to the bent portion in the CRT which includes a panel having a curvature radius of below 4 mm of an inner surface diagonal portion which is a corner portion, and a safety band bent at a mold match line of a side wall portion of the panel and continuously surrounding a side wall portion of the panel in the lengthy direction.